One of these is the notion of "free cooling," which, as far as marketing pitches go, is about as appealing as it gets. What's not to like about the ability to maintain comfortable operating temperatures at little or no cost?

Of course, as data center design consultant Robert McFarlane pointed out recently, free cooling isn't exactly free, just free-er compared to traditional HV/AC solutions. True, you don't have the expense of mechanically cooling the air or water coming from the heated IT environment, but you still need fans and/or pumps to move the heat load to wherever it can be dissipated, and that requires energy. And remember, there are very few locations with adequate infrastructure that can provide year-round free cooling, so you'll still need to invest in traditional methods to pick up the slack, or plan on shutting the facility down occasionally and shifting the load elsewhere.

Google has apparently crunched these numbers and has still come out in favor of a massive free-cooling design for its newest center in Hamina, Finland. The plan calls for drawing seawater from the Gulf of Finland a quarter-mile inland through a pre-existing tunnel to a data center built inside an old paper mill. The system utilizes a series of water-to-water cooling modules and a mixing facility that combines outgoing water with some of the incoming to ensure that the return is roughly equal in temperature to natural seawater.

With water being the heavy medium that it is, most organizations are likely to utilize one of the new air-cooling systems hitting the channel. A company called Airedale, for example, offers the ECHO system that cuts energy consumption by 67 percent compared to conventional systems, and even 46 percent compared to rival free-cooling systems. The setup utilizes a series of Active Cabinet Exhaust (ACE) units on the server racks tied to a series of free-cooling chillers, all governed by a monitoring/control system that manages load densities and other parameters at the rack level.

Of course, it's always easier to introduce more efficient cooling mechanisms when building data facilities from the ground up. That may become an even easier proposition with the introduction of new modular data centers preconfigured for energy-efficient operation. HP's new EcoPOD, for instance, is outfitted with direct expansion (DX) chillers to supply cold aisle service, but it can also be switched over to free-air mode that can pull upwards of 3,800 square feet of air per minute into the racks. The structure also provides a DX Assist mode that combines both functions.

No matter how it's accomplished, free cooling will always be preferable to conventional methods, but it will only be truly effective when Mother Nature is at her most cooperative. That means employing it when conditions are right will save you a lot of green, but over-reliance could end up costing you plenty as well.

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